Gear finishing machine



Feb. 3, 1953 w. s. PRAEG 2,627,141

GEAR FINISHING MACHINE Filed Nov. 8. 1948 2 SHEETS-SHEET 1 IKE-E IN V ENTORI WA rm 5. PRAEG BY WW [6% 77 78 8 Ar -0R 5 Feb. 3, 1953 w. s. PRAEGGEAR FINISHING MACHINE 2 SI'lEETS-SHEET 2 Filed NOV. 8. 1948 I y uINVENTOR. 4/7? S. PRA 6 A TI'OR/Vff Patented Feb. 3, 1953 GEAR FINISHINGMACHINE Walter S. Praeg, Detroit, Mich, assignor to Nav tional Broachand Machine Company, Detroit, Mich., a. corporation of MichiganApplication November 8, 1948, Serial No. 58,895

17 Claims.

The present invention relates to a gear finishing, and more particularlya gear lapping machine.

The process of finishing gears by running them inmesh at crossed axeswith agear-like lap has long been known but has not been widely adoptedfor several reasons. The first of these reasons is that as previouslypracticed, lapping has been a relatively slow process. The second reasonis that lapping tools are subjected to rapid wear so that as a resulttool cost was excessively high.

The present invention differs from prior known lapping practice inseveral particulars. In the first place, it involves a relative traversebetween the lap and gear which is in a direction diagonal to the axes ofboth lap and gear. It is found that this direction of relative traverseresults in a much more eiiicient finishing action and permits thesurfaces of the teeth of a gear to be finish lapped in a singlereciprocation.

In the second place, the present method involves as an essential featurethe initial contacting of the gear and lap under a relatively lightpressure followed by a locking step which looks the gear and tool inposition at a fixed center distance. This is to be distinguished fromtheprior practice in which the ultimate aim was to finish the teeth ofthe gear to an exact dimension. Thus in the case of an oversize gear thelap was subjected to heavy pressures which resulted in very rapid anddestructive wear. In the present case the gear is previously finished todesired dimensions with a high degree of accuracy. This is accomplishedpreferably by a gear shaving operation in which due allowance is madefor changes in dimension of the gear during a subsequent heat treatment.Accordingly, after the shaving and hardening steps the gears are withinthe dimensional. limits. However, within these limits. theremay be somevariation in size. According to the present invention: the teeth of thegear are subjected to a lapping action which is uniform as between gearsof different dimensions. Thus an oversize gear is not subjected to moresevere lapping than is an undersize gear.

With equipment available it has prior to the present invention beenimpossible to practice this method, for the reason that no gearfinishing machines were available in which the teeth of the gear and lapcould be brought intolight could not sense the desired light pressurecontact.

It is an object of the present invention to provide a gear finishingmachine and method characterized by the bringing together of a gear andlap under a substantially constant and relatively light pressure contactfollowed by a lapping operation in which the gear and lap are rotated inmesh at high speed and are relatively traversed in a direction whichoccupies a plane parallel to the axes of both gear and lap and whichdirection is preferably diagonal with respect to both of the axes.

It is a further object of the present invention to provide apparatus inwhich gear and lap supporting spindles are mounted for relative approachand separation and in which the movable spindle is mounted on arelatively light spindle support biased by a substantially constant andrelatively small force toward the other spindle, and which includesmeans for locking the spindles in a relative position determined bymeshed engagement between the teeth of a gear and gearlike lap carriedby-said spindles.

Other objects and features of the invention will become apparent as thedescription proceeds, especially when taken in con unction with theaccompanying drawings, wherein:

Figure 1 is a front elevation of a gear lapping machine constructed inaccordance with the present invention;

Figure 2 is a plan view, partly in section, of the movable gearsupporting table;

Figure 3 is a section on the line 33 of Figure 2;

Figure 4 is a section on the line 4-4 of Figure 3;

Figure 5 is a section on the line 5-5 of Fige ure 2; y

shown in Figure 3;

Figure 7 is an enlarged diagrammatic view of a rotary cam; and I,

Figure 8 is a fragmentary section showing a detail of the machine.

Referring first to Figure 1, the gear lapping machine comprises a'pedestal l0 provided with a forwardly projecting overhanging portion II,to the underside of which is mounted a lap supporting head l2.

axis .to permit variation-in the crossed axes angle between the gear andlap. A motor (not shown) is mounted in the portion H of the ma- Figure-6is an enlarged sectional view of parts The lap supporting head I2 ismounted for angular adjustment about a vertical chine and is adapted torotate the lap supporting spindle [3 through suitable mechanism.

Mounted for vertical adjustment on ways provided at the front of thepedestal I is a knee l5 having horizontal ways extending transversely ofthe machine. Mounted on these ways for back and forth reciprocation is acarriage 20. Located within the base of the machine is a mo or whichincludes drive means for effecting relatively slow reciprocation of thecarriage 20 and control means for the motor are provided includingsuitable switches having switch actuators 22 and 24 adapted to beengaged by adjustable dogs .26 and 28.

Mounted on the carriage 20 is a rocking subtable 30, a suitable trunnionconnection indicated at 32 being provided between the carriage 2i! andthe sub-table 30. The stationary base of the machine includes anadjustable cam indicated generally at 34 and a cam follower 35 ismounted on the rocking table. Releasable clamping means 36 and 33 areprovided for locking the sub-table 3B in intermediate position when itis not desired to employ the cam for rocking the platform. The uppersurface of the table terminates in a circular plate 40 provided withcircular T-slots (not shown) on which is mounted an angularly adjustabletable 42 which may be angularly adjusted about a vertical axis. Thetable 42 has a platform 50 connected thereto for relative-movementtoward and away from the head l2 and the platform 50 is also providedwith adjustable slots 52 for supporting head and tailstocks 53 and 54which include centers between which is mounted a work gear W.

In the operation of the machine a work gear W is mounted between thehead and ta-ilstocks 53 and 54 in position to mesh with the lap Lcarried by the head l2. The platform 50 is constructed so as to haverelatively slight movement toward and away from the head l2 and suitablemeans are provided for biasing the platform 50 toward the head [2 with asubstantially constant but relatively small force. When the teeth of thegear W and the lap L have come into light pressure contact as a resultof the biasing force aforesaid, the platform 50 is rigidly locked inposition, after which the gear lapping operation takes place. The gearlapping operation results from relatively rapid rotation of the gear andlap in mesh and reciprocation of the carriage 20.

During this operation the table 42 is in angularly adjusted position sothat the axis of the work gear W extends at an oblique angle withrespect to the direction of traverse of the carriage 20. Furthermore,the head I2 is angularly adjusted so that the lap will mesh with thework gear W with the axes of the gear and lap crossed at a limited angleas between 3 and 20.

In order to effect engagement between the teeth of the gear and lapunder light but substantially constant pressure contact as aforesaid,the detailed construction illustrated in Figures 2 to 6 is employed.Referring first to Fig ure 3, the platform 50 is pivoted to the table 42by a pivot pin 60. Adjacent the forward edge of the platform 50 areadjustable biasing springs 6|, best seen in Figure 5, these springsseating at their lower end against the table 42, which as previouslynoted is clamped in angularly adjusted position on the rocking table 30,suitable clamping bolts being shown at 62. A cup-shape adjusting plug 63is threaded into a threaded opening as shown. By means of theconstruction, a substantially constant biasing force is provided whichmay be adjusted so as to urge the platform upwardly so as to causecontact between the gear and lap to take place under uniform lightpressure conditions, independent of the actual position of the platformwhen contact is established.

Means are provided for rigidly locking the platform in adjustedposition. These means are for the most part located in a housing 64doweled and bolted to the forwardly extending free edge of the platform50. This housing includes a recess 65 (Figure 6) which receives aninverted U-shaped yoke 66 secured by bolts 61 (Figure 4) to the table42. Beneath the yoke 66 is a hardened wear plate 68.

Extending forwardly from the platform 50 is a camming and clampingstructure which is permitted limited up and down movement between theyoke 66 and plate 68.

This structure comprises an elongated threaded stud H3 rigidlyandnonrotatably mounted inthe forward edge of the platform 50. Rigidlyseated in a recess in the forward edge of the platform 56 is a wedgingelement 12, which as illustrated may be heldin place by stud 10. Element12 has upper and lower inclined surfaces 13 and 14 respectively.Threaded to the stud 7B for rotation and longitudinal motion thereon isa nut '15, hav ing pinion teeth 16, a cam 11 and a cylindrical orspherical end portion (8. A carrier plate 80, having a spherical seattherein interfitting with the spherical end portion 78 of the nut, isreceived between the nut and wedge element 12, and is provided with anenlarged bore 8| so that it may rock on its spherical seat. Plate 80 haspairs of forwardly projecting ears 82 carrying pins 83 on which rollers84 are mounted. The rollers 84 have substantial clearance with respectto pins 83, as illustrated, and are therefore radially movable thereon.

Cam 11, as best seen in Figure '7, has a high portion of uniform radiusbetween radii R2, a low portion of uniform radius between radii RI, andrise and fall portions between radii RI and R2. Bias spring 6| keeps theplatform elevated to keep cam l! in contact with the underside of yoke56 except when the teeth of the gear and lap depress the platform. Whenthe high portion of the cam between radii R2 is in contact with theyoke, the platform is depressed to loading position.

Referring again to Figure 2, an air cylinder 98 is supported by thehousing 54 and is provided with a piston connected to a piston rod 53!which is threaded or otherwise suitably secured to an actuating bar 92which is provided with rack teeth 93 at its underside which mesh withthe pinion teeth 76 formed on the nut 75.

With the cam I? in position such that the raised portion thereofintermediate the radii R2 is in contact with the underside of the crosspiece of the yoke 66, the platform 50 is in depressed or loadingposition. At this time a work gear W may be mounted between head andtailstocks 53. 54 and it will be in loose mesh with respect to the lapL. At this time the apparatus is in condition for initiation of anautomatic cycle. This cycle comprises initially admitting motive fluidto the cylinder which will cause the bar 92 to move to the right as seenin Figure 2, thereby rotating the nut 15. Initial rotation of the nutwill cause corresponding rotation of the cam ll formed thereon and willmove the elevated portion of the cam between radii R2 out of engagementwith the yoke 66 and will thus permit upward locking movement of theplatform 50 under the biasing force supplied by the compression springs6|. Upward movement of the platform 50 continues until the teeth of thework gearW and lap L come into light pressure contact, this contactbeing established by the adjustment of the compression springs 6 I. Theposition of the platform 50 when its upward motion is thus arrested willdepend upon the exact dimensions'of the work gear and thus may varybetween small limits.

It is essential in order that the subsequent lapping operation becarried out under suitable conditions for the platform to be rigidlylocked in position during the traverse strokes.

Rotation of the nut 15, in addition to moving the cam H as justdescribed, also advances the nut 15 to the right, as seen in Figures 3and. 6. Preferably the threads provided between the stud 16 and the nut15 have a substantial lead so that rotation of the nut in an amountbetween 45 and 225 will effect locking of the platform. Locking of theplatform is effected by causing the rollers 84 to be interposed inwedging or abutting relation between three angularly disposed surfaces.These surfaces are the upper and lower inclined surfaces I3 and 14 ofthe wedge member, the lower surface of the yoke 66, the upper surface ofthe wear plate 68, and the end surfaces of the carrier plate 80. If itso happens that the platform 50 and hence the stud I6 is in intermediateposition with respect to the yoke and wear plate, the rollers 84 willenter into locking engagement as described without rocking of thecarrier plate 80 on its spherical or cylindrical seat. If, however, thestud and associated mechanism is closer to either the underside of thecross piece of the yoke 66 or the upper surface of the wear plate 68,full locking engagement will not take place until the carrier plate 80has rocked on its seat 18 so as to cause one of the rollers 84 to moveforwardly and the other one to move rearwardly a corresponding amount.Inasmuch as the rollers 84 are loosely mounted on their carrier pins 83they accommodate themselves to the spaces in which they are received.Furthermore, since both of the rollers 84 are carried by a single rigidcarrier plate 86, it will be apparent that when the nut is advanced tothe right as seen in Figure 6 the full amount permitted before rigidengagement of the rollers 84 with the locking surfaces, a type oflocking will be obtained characterized by the interposition of rigidelements between relatively movable surfaces.

Since rotation of the nut element I5 is effected by an air cylinder,forward movement of the piston in the cylinder will be arrested when therollers 84 come into engagement with the locking surfaces. Preferablyautomatic controls are provided for thereafter initiating rotation ofthe lap and traverse of the carriage 20. The first stroke of traverse isarrested by operation of reversing switches having actuators such as 22or 24 which initiate a return stroke of traverse. Upon completion of thereturn stroke of traverse, rotation of the lap and gear is stopped andthe motive fluid is admitted to the cylinder so 'as to cause reversemovement of the piston therein. This will move the rollers 84 out oflocking engagement and will also rotate the cam I1 so as to bring theelevated portion thereof into engagement with the underside of the yokeelement. This has the result of moving the platform 50 downwardly so asto bring'the lapand work gear into, loose mesh, at which time thecompleted work piece may be removed. The present machine is designed tocarry out a lapping operation which is characterized by its short cycleand by the fact that it is intended to remove a substantially uniformamount of material from the teeth of a series of work gears independentof small variations in size between such work gears.

As previously stated, the operation is intended to be carried out withthe axis of the work gear W inclined to the direction of traverse of thecarriage 2B. This has two important results which make possible thepresent operation. In the first place, by properly selecting theangularity between the axis of the work piece and the direction oftraverse, it is possible to cause the finishing action between the lapand work piece to be distributed substantially from end to end of theteeth of the lap. This has the effect of greatly increasing lap life andpreventing localized wear on the lap teeth. At the same time it resultsin a more efficient lapping action which removes the requisite amount ofmaterial from the teeth of the gear without the necessity of repeatedreciprocations, as has been required in prior lap-.- ping methods.

A third result of the use of traverse in a direction diagonal to theaxis of the work gear is the gauging of the amount of material to beremoved from the teeth of the work gear by the simple expedient oflocating the work gear in a definite position relative to traverse whenit is moved upwardly into mesh with the teeth of the lap. If theposition of the work gear is such that the common normal to the axes ofthe lap and gear lies outside of the edges of the work gear, subsequenttraverse will bring the teeth of the lap and gear into mesh at a centerdistance which will predetermine the amount of material to be removedfrom the teeth of the lap. Accordingly, the present apparatus permits avery rapid sequence of operations which will result in the removal ofsubstantially identical amounts of material from the teeth of the workgears without requiring the careful attention of the operator. It isnecessary only for the operator to remove and replace work gears betweenthe head and tailstocks, the remainder of the operation being fullyautomatic.

It is particularly pointed out that the present method is not intendedprimarily for accurate control of final dimensions of the gear, sincethe final position of the work supporting platform 50 is determined bythe dimensions of the gear before lapping. Prior to the presentinvention one of the most important uses of gear lapping was in thereclamation of rejected gears. The present method is intended as aproduction step in the mass production of gears and contemplates thatthe lapping will be applied to all gears for th purpose of improvingsurface finishing and effecting correction of such gear characteristicsas profile, lead, concentricity, etc. Tests in production have shownthat'the present method improves the operating characteristics of gearsby a very considerable factor and since it is possible to carry out thisoperation at a high production rate, it makes production lapping apractical operation in the mass production of gears.

The foregoing description has been made with particular reference touse'of the machine as a gear lapping machine. However, it will bereadily appreciated that the inventionmay be practiced when gearfinishing toolsof different type are employed. Thus, for example, themachine may be used with a gear shaving toolin which the teeth of thgear-like tool are provided with edges and guiding lands. The principaldifierence between lapping and'shaving resides in the fact that the gearshaving operation is an accurate cutting operation in which a definiteamount of stock may be removed in a singl traverse of the gear and tool,whereas in lapping the material of the gear teeth is worn away by arubbing action.

The machine as illustrated in Figure 1 is ordinarily provided withmechanism for efiecting vertical adjustment of the knee l5 and the priorpractice has been to provide a plurality of reciprocations, at the endof each of which the knee may be fed upwardly by a small predeterminedamount so as to take a cut of corresponding amount on the teeth of thegear on the next stroke of traverse. The present invention may becombined with the machine including the vertical feed of the knee so asto carry out a new and improved method of finishing. Thus, for example,the gear and tool may be brought into light pressure contact aspreviously described, after which the first stroke of traverse may betaken. Upon completion of the first stroke of traverse and beforeinitiation of the return stroke, the knee may be feed upwardly by asmall predetermined amount. This method may if desired includeadditional strokes of traverse, although it is contemplated ordinarilythat the gear will be completely finished in two strokes of traverse ora single back and forth reciprocation of the parts.

The machine is further capable of carrying out another modified methodin which the air cylinder 90 is actuated at the end of the first strokeof traverse so that the platform 53 may move upwardly to a new positionso as to remove a definite amount of stock on the return stroke.Advantage may be taken of the automatic upward movement of the platform50 whenever the air cylinder is actuated to release the locking means toavoid the necessity of providing for automatic vertical adjustment ofthe knee I5. Thus, if the platform is designed to have sufficientvertical movement, a number of strokes of traverse may be taken with acorresponding removal of stock upon each stroke of traverse either byshaving or lapping and the final dimension of the gear may be determinedby providing an independent abutment which limits upward movement of theplatform 50.

Preferably suitable means are provided for initially positioning theplatform 50 in a predetermined intermediate position during setup of themachine for a run of gears.

This means may constitute merely witness marks brought into registry toindicate that the platform is in intermediate position. Preferably,however, it takes the form of a suitable locking means, such for exampleas a lug 98 projecting laterally from the yoke 66, and a hook bolt 99mounted in the housin 64 and having a projection I00 adapted to berotated to a position underlying lug 98, when the platform is in itsdepressed position. Spring pressed pin I0! is provided and is associatedwith recesses I02 in the bolt 99 to retain the bolt in operative orinoperative position as desired. The initial setup will then involvedepressing platform 50, rotating bolt 99 to bring projection I09 beneathlug 98, releasing platform 59 to permit it to rise to the intermediateposition determined by engagement between lug 98 and projection I99,loading a work gear between the stops 53 and 54, and vertical adjustmentof the knee IE to bring the gear and tool into mesh and preferably intolight contact. Thereafter if an oversize gear is inserted the platform50 may be depressed to a position below the initial set position asdetermined by the locating means, and if an undersize gear is presentthe platform will come to rest in a position above the positiondetermined by the locating means. If a carefully checked or master gearis used in the initial setup it will insure that the average position ofthe platform during the first shaving stroke of traverse will be thepredetermined intermediate position as set by the locating means. Theupper surface of projection I00 may if desired be an inclined cammingsurface so that diiferent rotational position of bolt 99 willpredetermine different positions in which platform 50 is locked duringinitial setup.

The drawings and the foregoing specification constitute a description ofthe improved gear finishing machine in such full, clear, concise andexact terms as to enable any person skilled in the art to practice theinvention, the scope of'whic i indicated by the appended claims. I

What I claim as my invention is 1. A gear finishing machine comprising aframe, a rotary spindle on said frame, a relatively massive slidemovable on said frame toward and. away from said spindle, a relativelylight spindle support carried by said slide movable toward and away fromsaid spindle, a second spindle on said spindle support, said spindlesbeing relatively angularly adjustable, means for eifecting relativetraverse between said spindles in a direction to cause distribution offinishing action longitudinally of the teeth of a gear mounted on onespindie by a gear-like tool mounted on the other spindle, motive meanseffective to urge said spindle support toward said first spindle with aconstant relatively small force to mesh a gear and lap on said spindles,and clamping means for clamping said spindle support in the position itis in when the gear and lap are in contact.

2. Apparatus as defined in claim 1 in which the motive means isadjustable sprin means.

3. Apparatus as defined in claim 1 in which the s indle support ispivoted at one edge, and the motive means and clamping means are locatedat the opposite edge thereof.

4. In apparatus of the character described, a spindle support movabletoward and away from a spindle, means biasing said support toward saidspindle, locking mean effective to lock said support in any position,said locking means comprising fixed means providing a pair of opposedsurfaces, wedging means movable with said sup port providing a pair ofinclined surfaces between said opposed surfaces, a pair of lockingmembers of circular cross section loosely received respectively betweeneach of said inclined surfaces and the adjacent one of the opposed surfaces, and a rocking member movable toward-said wedging means for movingboth of said locking members into locking relation between the surfacesadjacent thereto.

5. Apparatus as defined in claim 4 provided further with cam means formoving said spindle support away from said spindle.

' 6. Apparatus as defined in claim 5 provided further with means foractuating said cam means to release said support for movement towardsaid spindle and for moving said rocking member toward said wedgingmeans. i v

- '7. In a gear finishing-machine, a first spindle,- a spindle supporthinged at one side and movable toward and away from said first spindle,a second spindle on said support, resilient means at the free side ofsaid support effective to urge said support toward said first spindlewith a relatively small constant force, and power actuated means forrigidly locking said support in any intermediate position determined bymeshed engagement of a gear and lap carried by said spindles withoutaffecting the spacing between said spindles, said locking meanscomprising a member movable between opposed surfaces, said member andsurfaces defining a pair of spaces of varying width, an abutment memberin each of said spaces, and a rigid member engageable with both of saidabutment members to effect positive movement of said members intolocking position.

8. In a gear finishing machine, a first spindle, a spindle supporthinged at one side and movable toward and away from said first spindle,a second spindle on said support, resilient means at the free side ofsaid support effective to urge said support toward said first spindlewith a relatively small constant force, and power actuated means forrigidly locking said support in any intermediate position determined bymeshed engagement of a gear and lap carried by said spindles withoutaffecting the spacing between said spindles, said locking meanscomprising a first member providing a pair of opposed surfaces, a secondmember relatively movable in a direction generally perpendicular to saidsurfaces, said second member and said surfaces defining spaces atopposite sides of said member which are tapered in a directionperpendicular to the direction of relative motion between said members,a rigid abutment member in each of said spaces, and a rigid elementengageable with said abutment members, said element being rockablymounted and movable to effect positive advance of said abutment elementsinto locking position.

9. A machine as defined in claim 8 in which cam means are provided formoving said hinged support away from said first spindle.

10. A machine as defined in claim 9 in which power means are providedfor sequentially operating said cam means for releasing said spindlesupport for motion toward said first spindle, and for advancing saidrigid member to look said spindle support in place.

11. In a gear finishing machine, a first spindle, a spindle supportmovable toward and away fromsaid first spindle, a second spindle on saidsupport, means operable to bias said spindle support toward said firstspindle, cam means operable to move said spindle support away from saidfirst spindle, and power actuated rigid abutment means operable to locksaid spindle support in any intermediate position as determined byengagement between a gear and gear-like tool carried by said spindles.

12. In a gear finishing machine as defined in claim 11, power meansoperable to effect sequential movement of said cam means to release saidsupport, and movement of said abutment means to lock said support.

13. A gear finishing machine comprising a frame, an angularly adjustablehead on said frame, a spindle on said head, a slide movable on saidframe toward and away from said head, a carriage on said slide, aspindle support on said carriage pivoted thereto at one edge formovement toward and away from said head, means for biasing said supporttoward said head, a yoke on said carriage at the free edge of saidspindle support, a wedge-shaped member on the free edge of said spindlesupport movable transversely of said yoke, loosely mounted rollersbetween said wedge-shaped member and the adjacent surfaces of said yoke,and a rockable member engageable with said rollers and movable towardand away from said wedge-shaped member.

14. A machine as defined in claim 13, comprising cam means operable tomove said spindle support away from said head, and power means forsequentially operating said cam means and said rockable member.

15. A gear finishing machine comprising a pair of spindles, means forrotating one of said spindles, means for relatively traversing saidspindles parallel to a plane parallel to the axes of both spindles, oneof said spindles being movable toward and away from the other spindle,resilient means operably associated with said one spindle effective tomove said one spindle toward the other with a relatively small constantforce, cam means for moving said one spindle away from the other againstthe action of said resilient means, and means for rigidly locking saidone spindle in any intermediate position of its movement toward saidother spindle, said locking means comprising relatively stationary meansproviding a pair of confronting surfaces, 2. pair of abutment elementsengageable with said surfaces, and wedging means movable with said firstspindle effective to force said parts against said surfaces, saidelements being relatively movable and said wedging means being rockableto pro vide for movement of one of said elements into locking engagementwith the adjacent surface after the other of said elements has engagedits adjacent surface.

16. A gear finising machine comprising a pair of spindles, means forrotating one of said spindles, means for relatively traversing saidspindles parallel to a plane parallel to the axes of both spindles, oneof said spindles being movable toward and away from the other spindle,resilient means operably associated with said one spindle effective tomove said one spindle toward the other with a relatively small constantforce, cam means for moving said one spindle away from the other againstthe action of said resilient means, and means for rigidly locking saidone spindle in any intermediate position of its movement toward saidother spindle, said locking means comprising a nut, a threaded shaftmovable with said first spindle on which said nut is mounted, meansassociated with said nut and dependent on axial advance thereof tooperate said locking means, said cam means including a cam surface onthe periphery of said nut.

17. A machine as defined in claim 16 comprising an actuator for rotatingsaid nut to operate said cam means and to operate said locking means insequence.

WALTER. S. PRAEG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 675,936 Dawson June 11, 19012,335,215 Schurr Nov. 23, 1943 2,380,208 Ashton July 10, 1945 2,385,129Davis Sept. 18, 1945 2,387,679 Praeg Oct. 23, 1945 2,433,468 Mackmann eta1. Dec. 30, 1947 2,435,405 Praeg Feb. 3, 1948 2,582,408 Bauer Jan. 15,1952

